Field of the Disclosure
The present invention relates to a process for hydroprocessing a hydrocarbon feed and more particularly to a process for hydroprocessing a gas oil hydrocarbon feed.
Description of Related Art
Global demand for diesel has risen quickly with increased growth of transportation fuels. At the same time, regulations on the properties of the transportation diesel have become more rigorous in order to mitigate environmental impact. European standard Euro IV (EN590:1993) for diesel fuel set a maximum density of 860 kilograms per cubic meter (kg/m3). More recently, under Euro V (EN 590:2009) the maximum density was reduced to 845 kg/m3. Other properties for transportation diesel include a polycyclic aromatics content of less than 11 wt % and, under Euro IV, a sulfur content of less than 20 part per million by weight (wppm), reduced to 10 wppm under Euro V, which is sometimes referred to as ultra-low-sulfur-diesel, or ULSD.
Refineries produce a number of hydrocarbon products having different uses and different values. It is desired to reduce production of, or upgrade, lower value products to higher value products. Lower value products include gas oils. Gas oils have historically been used as feedstocks for producing higher grade (value) refinery products. Such oils cannot be directly blended into today's transportation fuels (gasoline and diesel fuel pools) because their high sulfur content, high nitrogen content, high aromatics content (particularly high polyaromatics), high density, and low cetane value do not meet government standards for the United States and European countries.
In addition, when gas oils are used as feedstocks for producing diesel fuel, yield of diesel range product is less than desired. Nonetheless, it is desired to use gas oil as a feedstock to produce diesel fuel, including ULSD.
Various hydrotreating methods, such as hydrodesulfurization and hydrodenitrogenation, can be used to remove sulfur and nitrogen from a hydrocarbon feed. Hydrocracking can be used to crack heavy hydrocarbons (high density) into lighter products (lower density) with hydrogen addition. However, high nitrogen content can poison a zeolitic hydrocracking catalyst, and hydrocracking conditions which are too severe can cause the formation of significant amounts of naphtha and lighter hydrocarbons which are considered lower value products than transportation fuels.
Conventional hydroprocessing units used for hydrotreating and hydrocracking have three-phase (trickle bed reactors) which require hydrogen from a vapor phase to be transferred into liquid phase where it is available to react with a hydrocarbon feed at the surface of the catalyst. These units are expensive, require large quantities of hydrogen, much of which must be recycled through expensive hydrogen compressors, and result in significant coke formation on the catalyst surface and catalyst deactivation.
U.S. Pat. No. 6,123,835, discloses a two-phase (“liquid-full”) hydroprocessing system having a liquid-full reactor which avoids some of the disadvantages of trickle bed systems.
U.S. Patent Application Publication 2012/0205285 discloses a two-stage hydroprocessing process for targeted pretreatment and selective ring-opening in liquid-full reactors with a single recycle loop to convert heavy hydrocarbons and light cycle oils to liquid product having over 50% in the diesel boiling range.
U.S. Patent Application Publications US 2012/0080288 A1 and US 2012/0080356 A1 disclose an apparatus and a process, respectively, for hydroprocessing a hydrocarbon feedstock with hydrogen in a first and second hydroprocessing zones wherein the effluent from the first hydroprocessing zone is fractionated on a first side of a dividing wall fractionation column to provide a diesel stream and wherein at least a portion of the diesel stream is the feed to the second hydroprocessing zone. Thus, a diesel fraction is further subjected to hydrogen, increasing yield of lower boiling fractions, such as naphtha, while reducing diesel yield.
Still, it is desirable to provide hydroprocessing systems which convert heavy hydrocarbon feeds, in particular gas oils, to diesel in higher yield and/or quality.